使用ANT时，如果我有一些特定的java版本，我怎么才能定义一个任务？

I have the problem that an specific step in Ant can only be executed when we have Java 1.5 installed in the build computer. The task definition uses uses a jar file that was compiled using 1.5, so running with a 1.4 virtual machine will throw an IncompatibleClassVersion exception.I have the problem that an specific step in Ant